The invention relates to an electronic apparatus incorporating a multiplicity of semiconductor integrated circuits (ICs) arranged on an substrate which operate at different operating voltages and a semiconductor IC for use in such electronic apparatus.
Recent advance in semiconductor technology has enabled fabrication of large scale integrated (LSI) semiconductor circuits. The maximum allowable level of the operating voltage for such LSI is limited more than ever to a lower operating voltage, for example from conventional 5 Volts to 3 Volts or to an even lower voltage of 2 Volts. Besides, a multiplicity of LSIs used in an electronic apparatus often have different operating voltages. In order to allow transmission of signals between two LSIs running at two different operating voltages, an interface is required to adjust or absorb the difference in the operating voltages.
Conventionally, adjustment of the voltages is done by converting the lower operating voltage of one LSI to a higher voltage to match with the operating voltage of other conventional (mostly well established) LSI.
Consequently, for an electronic apparatus having a multiplicity of LSIs which are operated at different operating voltages, it is a common practice to raise the lower voltage (2 Volts for example) of the interface section of the LSIs to the higher operating voltage of the other LSI by making oxide layers of the gates thicker or making the channels longer, or by utilizing dedicated special transistors.
However, these resolutions inhibit high-degree integration of low voltage LSIs, sacrificing the merit of up-to-date large scale integration technology, and resulting in not only increase of chip areas but also additional complexity to the manufacturing processes, and hence increases production cost of the electronic apparatus.
In accordance with one aspect of the invention, there is provided an electronic apparatus incorporating a multiplicity of operably connected semiconductor integrated circuits (ICs) arranged on a substrate which operate at different operating voltages, wherein all the interface voltages between operably connected ICs are set to the lowest operating voltage.
Each of the ICs other than those operating at the lowest operating voltage is provided with:
an input circuit for converting the lowest operating voltage of a signal input thereto from another IC to its own operating voltage; and
an output circuit for converting the voltage of the signal to be output therefrom to the lowest operating voltage.
In accordance with another aspect of the invention, there is provided an electronic apparatus incorporating a multiplicity of operably connected semiconductor integrated circuits (ICs) arranged on a substrate which operate at different operating voltages, wherein
the interface voltage between any two operably connected ICs operating at two operating voltages is the lower operating voltage of the two.
Each of the ICs other than those operating at the lower operating voltage is provided with:
an input circuit for converting a lower operating voltage of a signal input thereto from another IC to its own operating voltage; and
an output circuit for converting the voltage of the signal to be output therefrom to a required lower operating voltage.
In this arrangement, although the electronic apparatus incorporates a multiplicity of LSIs that operate at different operating voltages, the most highly integrated IC having the lowest operating voltage can be interfaced with its own operating voltage, so that the electronic apparatus can enjoy the merit of the large scale integration.
It is noted that those LSIs not operating at the lowest operating voltage can be interfaced with other LSIs at a lower voltage than their own operating voltages using input/output circuits.
Since the interfacing is done at a low voltage, energy loss due to electromagnetic interference (EMI) for example can be reduced accordingly.
If all the interface voltages for the operably connected LSIs are set to the lowest operating voltage of the LSIs, then all the LSIs can be interfaced through the their input and output circuits connected at the same lowest voltage, thereby simplifying the design of the input/output circuits.
When the interface voltage for any two operably connected LSIs operating at two different operating voltages is set to the lower one of the two, the LSI having a lower operating voltage needs no input circuit or output circuit, thereby advantageously reducing the number of input/output circuits.